Engine Fuel injection timing control apparatus

ABSTRACT

This invention relates to an engine fuel injection timing control apparatus for controlling a fuel injection timing by adjusting the position of a timer piston via a solenoid valve. In this apparatus, a frequency signal switching means (44) selectively outputs a first frequency signal (W1) and a second frequency signal (W2) having a frequency lower than the first frequency signal (W1) according to an engine speed (Ne) detected by an engine rotational speed detecting means (49) with reference to preset signal switching engine rotational speeds (N 1 , N 2 , N 3 , N 4 , N 5 ). With a driving frequency based on thus outputted frequency signal, a control means (46) duty-controls a timer controlling solenoid valve (39) according to an engine operation state. Here, the signal switching engine rotational speeds (N 1 , N 2 , N 3 , N 4 , N 5 ) are set to levels which yield first predetermined rotational speed differences (U 1 , U 2 , U 3 , U 4 , U 5 ) from engine rotational speeds where the resonance is generated with respect to a first frequency (f 1 ) and second predetermined rotational speed differences (L 1 , L 2 , L 3 , L 4 , L 5 ) from engine rotational speeds where the resonance is generated with respect to a second frequency (f 2 ). Consequently, the fluctuation phenomenon of the timer piston can securely be suppressed in the vicinity of resonance points.

This application claims the benefit under 35 U.S.C. §371 of prior PCTInternational Application No. PCT/JP96/01768 which has an Internationalfiling date of Jun. 26, 1996 which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreferences.

TECHNICAL FIELD

This invention relates to an engine fuel injection timing controlapparatus which is suitably used for controlling a fuel injection pumpof a diesel engine and, in particular, to an engine fuel injectiontiming control apparatus which can control a fuel injection timing byadjusting the position of a timer piston via a solenoid valve.

BACKGROUND ART

Known as a fuel injection pump for a diesel engine is the one having aconfiguration shown in FIG. 4. The fuel injection pump shown in FIG. 4is a so-called distributor type fuel injection pump based on anelectronic control system. In FIG. 4, 10 refers to a pump main body, anda vane type feed pump 11 is disposed within the pump main body 10. Here,as for the feed pump 11, together with its original side view, a frontview with an angle of representation changed by 90° is also shown.

The feed pump 11 is rotated by a drive shaft 12 which is actuated as theengine rotates, thereby forcibly feeding fuel from a fuel tank. The fuelemitted from the feed pump 11 is transmitted to a pump chamber 13 withinthe pump main body 10, and then is supplied therefrom to a fuel forcedfeed plunger 15 through a passage 14. Inserted into the passage 14 is afuel cutting magnet valve 16.

The plunger 15 supplies, by way of a communicating hole 17A formedtherein, fuel from the passage 14 to a delivery valve 19 through apassage 18, while moving back and forth within a plunger chamber 17formed in the pump main body 10. Such back and forth movement of theplunger 15 is effected by a cam disc 20 connected to one end of theplunger 15.

Namely, the plunger 15 and the cam disc 20 are rotated by the driveshaft 12 in response to the engine rotation. Also, the cam disc20 isurged by a spring 21 via the plunger 15, thereby abutting to a roller 23axially supported by a roller holder 22. Here, the roller holder 22 doesnot move in the axial direction of the drive shaft 12 and usually(except for the time when rotational phase is being adjusted, which willbe explained later) does not rotate around the axis of the drive shaft12. Consequently, the cam disc 20 moves in the axial direction whilebeing shoved by the roller 23 according to its cam profile. Thus, theplunger 15 moves back and forth, thereby supplying fuel at a desiredtiming.

Here, each cylinder is provided with the passage 18 and the deliveryvalve 19. For example, in the case of a four-cylinder engine, fourpieces each of passages 18 and delivery valves 19 are provided.

As shown in FIGS. 5, the roller holder 22 is provided with a pluralityof rollers 23 (which are four here), and the cam disc 20 has a camprofile corresponding thereto. Consequently, as the cam disc 20 makesone revolution, the plunger 15 is driven four times, whereby, forexample, fuel is successively supplied to four cylinders respectively inresponse to these four driving operations of the plunger 15.

Here, provided for fuel injection amount control are a control sleeve24, which moves back and forth on the outer periphery of the plunger 15so as to adjust the forced feed stroke of the plunger 15, and a governor(electric governor here) 25 for controlling the control sleeve 24.

Further, in FIG. 4, 26 is a regulator valve, 27 is a sensing gear platefor detecting the rotational speed of the drive shaft 12, 28 is a fueltemperature sensor, and 29 is an overflow valve, provided with a checkvalve, for returning excess fuel within the pump chamber 13 to the fueltank.

In order to control the fuel injection timing, such a fuel injectionpump is provided with a timer 30. The timer 30 is equipped with a timerpiston 31 for changing the position of the roller 23 in its rotatingdirection. Here, for convenience, the timer piston 31 is also depictedby a front view whose angle of representation is changed by 90°.

As shown in FIGS. 4, 5(A), and 5(B), the timer piston 31 minutelyrotates the roller holder 22 via a piston pin 33 while moving back andforth within a cylinder 32 formed in the pump main body 10.

Namely, the timer piston 31 has an intermediate portion to which thepiston pin 33 is connected, one end provided with a first pressurechamber 34 into which the fuel pressure within the pump chamber 13 isintroduced, and the other end provided with a second pressure chamber 35into which the intake-side fuel pressure (fuel pressure upstream thefeed pump 11) is introduced.

Also, the timer piston 31 is provided with a passage 36 through whichthe pump chamber 13 and the first pressure chamber 34 communicate witheach other, and the passage 36 is formed with an orifice 37. Further,disposed within the second pressure chamber 35 is a timer spring 38 forurging the timer piston 31 toward the one end (toward the first pressurechamber 34).

Hence, the position of the timer piston 31 is determined according tothe balance among the fuel pressure within the first pressure chamber34, the fuel pressure within the second pressure chamber 35, and theurging force of the timer spring 38. For example, when the fuel pressurewithin the first pressure chamber 34 becomes higher than that in thestate shown in FIG. 5(A), the timer piston 31 moves to the left in thedrawing as shown in FIG. 5(B), whereby the fuel injection timing isadjusted to the advancing side. When the fuel pressure within the firstpressure chamber 34 becomes low, by contrast, the timer piston 31 movesto the right in the drawing, whereby the fuel injection timing isadjusted to the retarding side.

For example, when the rotational speed of the engine becomes high, theoutput pressure from the feed pump 11 increases, whereby the fuelpressure within the pump chamber 13 also increases, thus yielding a highpressure within the first pressure chamber 34. Consequently, the timerpiston 31 moves to the left in the drawing, so that the fuel injectiontiming is adjusted to the advancing side.

Further, as shown in FIG. 4, disposed in the case of this pump is atiming control valve (TCV) 39 which can adjust the pressure balancebetween the first pressure chamber 34 side and the second pressurechamber 35 side, whereby the fuel injection timing can be adjusted onthe basis of various parameters.

Namely, the timing control valve 39 is a solenoid valve of electroniccontrol type, whose opening (valve opening time per unit time) isadjusted by duty control. Accordingly, as the timing control valve 39 isduty-controlled, the pressure difference between the pressure on thefirst pressure chamber 34 side and the pressure on the second pressurechamber 35 side is appropriately adjusted (to the reducing side here)according to the opening of the valve 39, thus regulating the positionof the timer piston 31, whereby the fuel injection timing is adjusted.

Such driving of the timing control valve 39 is effected by anon-depicted timing control valve driver (TCV driver), whose operationis controlled by a non-depicted controller according to a target fuelinjection amount Q and an engine rotational speed (i.e., number ofengine revolution per unit time, which will be hereinafter referred toas engine speed) Ne.

In the case where the timing control valve 39 is duty-controlled, suchcontrol is effected while driving current pulses are emitted at apredetermined frequency. When this driving frequency approaches anintegral multiple of the engine speed, the fuel injection timing mayfluctuate. This phenomenon is known as "fluctuation," which is supposedto be a phenomenon of so-called "beats" caused by interference of twodifferent frequencies close to each other.

For example, FIG. 6 shows experimental data concerning this fluctuationphenomenon, in which results of an experiment under a condition wherethe engine speed Ne is in the vicinity of 1,800 rpm and the drivingfrequency of the timing control valve 39 is 60 Hz. In FIG.6, theabscissa and ordinate respectively indicate time and position of thetimer piston 31 (TPS), whereas curve S indicates a fluctuationcharacteristic of the TPS, from which it can be seen that the TPS isvibrating with a relatively long period (about 1 second).

It is supposed that, while the driving frequency of the timing controlvalve 39, i.e., 60 Hz, becomes just twice that of the engine speed Newhen the latter is exactly 1,800 rpm (=30 Hz), such a phenomenon as"beats" occurs due to the fact that the engine speed Ne is close to butnot exactly 1,800 rpm.

Thus simulated is a case where the engine speed Ne is 1,700 rpm (=29.5Hz) while the driving frequency of the timing control valve 39 is set to60 Hz, which yields, as shown in FIG. 7, a characteristic substantiallythe same as the experimental results shown in FIG. 6.

When the orifice 37 constantly acts, and the opening of the timingcontrol valve 39 is kept constant, the inflow/outflow of fuel in theindividual pressure chambers 34 and 35, i.e., the position of the timerpiston 31, is ruled by the pressure difference between both ends of thetimer piston 31. Accordingly, changes in pressure difference aresupposed to cause the fluctuation (i.e., displacement of the timerpiston 31).

Further, presumed to be factors for changes in pressure difference arepressure changes in the pump chamber 13 and pressure changes in thecylinder 32 of the timer piston 31.

The pressure may change in the pump chamber 13 due to changes in thedischarge pressure of the feed pump 11, spills of the fuel forcibly fedby the plunger 15, and the like. Also, the pressure may change in thetimer piston cylinder 32 due to the fact that the reaction forcegenerated when the cam disc 20 runs over the roller 23 is transmittedthrough the piston pin 33, due to the resonance generated between themass of the timer piston 31 and the elastic property of the timer spring38, and the like.

Among them, particularly influential is the reaction force generated bythe cam disc when it runs over. Simply put, this reaction force is twiceas influential as the change in pressure of the pump chamber 13, sincethe inflow pressure changes at both ends of the timer piston 31 (i.e.,in both pressure chambers 34 and 35) when the cam disc runs over. Also,it can be considered most influential since the forced pressure actingon the timer piston 31 itself fluctuates greatly. In the case of afour-cylinder engine, the reaction force generated by the cam disc whenit runs over has a frequency twice that of the engine speed Ne and asubstantially constant amplitude.

In order to eliminate such a fluctuation phenomenon, the following meanscan be considered:

(1) Namely, as indicated by lines L1, L2, and L3 in FIG. 8, the drivingfrequency of the timing control valve 39 is completely synchronized witha resonance point with respect to the engine rotation, i.e., the enginespeed Ne, the level twice as high as the engine speed Ne (=2Ne), or thelevel four times as high as the engine speed Ne (=4Ne). This techniqueis disclosed, for example, in Japanese Patent Publication No. SHO63-8298.

(2) The driving frequency of the timing control valve 39 is preventedfrom approaching the resonance point with respect to the enginerotation, i.e., the engine speed Ne, 2Ne, or 4Ne, while being changedwith respect to the engine speed Ne like sawteeth as indicated by dottedline L4 in FIG. 8. This technique is disclosed, for example, in JapanesePatent Publication No. HEI 1-19059.

These means are based on a characteristic in which the greater is thefrequency difference between the timing control valve and the engine,the smaller becomes the fluctuation (piston amplitude). In FIG. 9, acharacteristic indicated by Ne refers to a case in the vicinity of the0.5-order resonance point, i.e., where the driving frequency of thetiming control valve is set near the engine speed Ne; that indicated by2*Ne refers to a case in the vicinity of the first-order resonancepoint, i.e., where the driving frequency of the timing control valve isset near the level twice as high as that of the engine speed Ne; andthat indicated by 4*Ne refers to a case in the vicinity of thesecond-order resonance point, i.e., where the driving frequency of thetiming control valve is set near the level four times as high as that ofthe engine speed Ne.

Regarding the solving means (1), the above-mentioned Japanese PatentPublication No. SHO 63-8298 relates to a technique in which theoperating frequency of an opening/closing valve (timing control valve)is controlled, according to the fuel feed pressure, so as to become anintegral multiple (e.g., twice that) of the engine speed, therebysynchronizing the operating period of the opening/closing valve with thepressure-changing period in the fuel feed pressure, thus decreasing thefluctuation in fuel feedpressure and accurately controlling the fuelinjection timing.

In this technique, however, since the fuel feed pressure is detected soas control the operation of the opening/closing valve on the basis ofthus detected pressure, there are disadvantages as follows:

First, as to the above-mentioned fluctuation phenomenon, the controlbased on the fuel feed pressure is not always appropriate since the fuelfeed pressure is relatively less influential.

Also, the timing for starting the driving of the opening/closing valvechanges every time the fuel injection timing changes, thus complicatingthe setting for the timing for terminating the driving of theopening/closing valve (i.e., duty width). When the driving terminatingtiming for the opening/closing valve is to be synchronized with therotational phase, on the other hand, the driving starting timing for theopening/closing valve cannot be set correctly, whereby the openingcontrol of the opening/closing valve (i.e., duty control) cannot beachieved.

Further, there is needed a contrivance for synchronizing the signalbased on the detected fuel feed pressure with the crank angle of theengine. It is due to the fact that the rise of fuel feed pressuresynchronizes with the injection timing but does not relate to the crankangle, and that the fall of fuel feed pressure depends on the amount ofinjection but does not relate to the crank angle either.

In the technique of (2), while a plurality of driving frequencies areselected according to the engine speed (rotational speed), the effect ofsuppressing the fluctuation phenomenon cannot securely be obtainedunless points for switching the driving frequencies are appropriatelyset.

For example, in a switching point P1 within the first-order resonanceregion in the vicinity of the line L2 in FIG. 8, the driving period ofthe timing control valve and the engine speed approach the first-orderresonance region, whereby the above-mentioned fluctuation phenomenontends to occur greatly. It is due to the fact that the piston amplitudecaused by fluctuation becomes greater in the first-order resonanceregion.

Namely, as indicated by the characteristic line 2*Ne in FIG. 9, thepiston amplitude in the vicinity of the first-order resonance issubstantially twice as large as that in the vicinity of the 0.5-orderresonance (characteristic line Ne) and nearly four times as large asthat in the vicinity of the second-order resonance (characteristic line4*Ne).

Thus, the greater the piston amplitude is, the lower becomes theaccuracy in controlling the fuel injection timing. Accordingly, thefluctuation phenomenon in the first-order resonance region should beeliminated in particular. The prior art has conceived no particularmeans against such fluctuation in the first-order resonance region, thusfailing to securely attain the effect of suppressing the fluctuationphenomenon.

Though Japanese Patent Application Laid-Open (Kokai) Nos. HEI 1-300037and 4-347346, and Japanese Patent Publication No. HEI 3-25626 eachdisclose a technique concerning the fuel injection timing control forengines such as diesel engine, they fail to specifically take account ofthe fluctuation phenomenon such as that mentioned above and cannotappropriately eliminate such fluctuation phenomenon.

In view of the problems mentioned above, it is an object of the presentinvention to provide, in an apparatus which can control a fuel injectiontiming by adjusting the position of a timer piston via a solenoid valve,an engine fuel injection timing control apparatus which can securelyattain an effect of suppressing the fluctuation phenomenon, thusallowing the fuel injection timing to be controlled appropriately.

DISCLOSURE OF THE INVENTION

To this end; in an engine fuel injection control apparatus comprising atimer for changing a fuel injection timing of an engine injecting fuelfrom a fuel injection valve by moving a timer piston in response to anoil pressure supplied thereto and a timer controlling solenoid valve foradjusting the oil pressure supplied to the timer as being opened andclosed by a driving signal having a duty cycle which is set according toan operation state of the engine, in which a resonance occurring in thetimer piston between driving by the timer controlling solenoid valve anda fluctuation accompanying a rotation of the engine is eliminated by achange in frequency of the driving signal of the timer controllingsolenoid valve; the engine fuel injection timing control apparatus ofthe present invention comprises first frequency signal generating meansfor generating and emitting a signal having a first frequency, secondfrequency signal generating means for generating and emitting a signalhaving a second frequency which is lower than the first frequency,engine rotational speed detecting means for detecting a rotational speedof the engine, frequency signal switching means for selectivelyoutputting the first frequency signal emitted from the first signalgenerating means and the second frequency signal emitted from the secondsignal generating means according to the engine rotational speeddetected by the engine rotational speed detecting means, and controlmeans, having a driving frequency based on the frequency signaloutputted from the frequency signal switching means, for controlling thetimer controlling solenoid valve by using the driving signal having theduty cycle that is set according to the operation state of the engine,wherein the frequency signal switching means is configured so as tochange over between the first frequency signal and the second frequencysignal according to a preset signal switching engine rotational speed,and wherein the signal switching engine rotational speed is set to alevel which yields a first predetermined rotational speed differencefrom an engine rotational speed where the resonance is generated withrespect to the first frequency and a second predetermined rotationalspeed difference from an engine rotational speed where the resonance isgenerated with respect to the second frequency.

Due to such a configuration, the fuel injection timing from the fuelinjection valve is adjusted when the timer moves the timer piston. Here,the timer piston operates while the oil pressure supplied thereto isadjusted by the timer controlling solenoid valve that is beingduty-controlled. While a driving force is periodically supplied from thetimer controlling solenoid valve to the timer piston, a pressure changeaccompanying the engine rotation is added thereto, whereby a resonanceoccurs between the driving by the timer controlling solenoid valve andthe fluctuation (pressure change) accompanying the engine rotation.Accordingly, the frequency of the driving signal of the timercontrolling solenoid valve is changed so as to prevent such a resonancestate from occurring.

Namely, the frequency signal switching means selectively outputs thefirst frequency signal emitted from the first signal generating meansand the second frequency signal emitted from the second signalgenerating means according to the engine rotational speed detected bythe engine rotational speed detecting means with reference to the presetsignal switching engine rotational speed, and the control means controlsthe driving of the timer controlling solenoid valve in response to thusoutputted frequency signal.

Here, since the signal switching engine rotational speed is set to alevel which yields a first predetermined rotational speed differencefrom an engine rotational speed where the resonance is generated withrespect to the first frequency and a second predetermined rotationalspeed difference from an engine rotational speed where the resonance isgenerated with respect to the second frequency, the fluctuation (beats)or resonance of the timer piston can be eliminated in the case where theengine rotational speed approaches the first or second frequency.Consequently, changes in fuel injection timing due to the fluctuation ofthe timer piston can be suppressed, whereby the fuel injection timingcan be accurately controlled, thus contributing to improving engineperformances.

Here, the first and second predetermined rotational speed differencesmay be either identical to or different from each other.

Also preferably, the signal switching engine rotational speed isdisposed between a first-order resonance region which is an enginerotational speed region where the resonance becomes a first-orderresonance and a secondorder resonance region which is an enginerotational speed region where the resonance becomes a second-orderresonance, and the frequency signal switching means outputs the secondand first frequency signals respectively in an engine rotational speedregion on the first-order resonance region side of the signal switchingengine rotational speed and in an engine rotational speed region on thesecond-order resonance region side of the signal switching enginerotational speed.

Consequently, the fluctuation or resonance of the timer piston in thefirst-order and second-order resonance regions can be eliminated.

Preferably, in this case, the signal switching engine rotational speedis set such that a rotational speed difference from a first-orderresonance engine rotational speed where the first-order resonance occurswith respect to the first frequency is greater than a rotational speeddifference from a second-order resonance engine rotational speed wherethe second-order resonance occurs with respect to the second frequency.

Consequently, the fluctuation or resonance of the timer piston can beeliminated efficiently in the first-order resonance region where thedemand for suppressing the fluctuation or resonance is relatively high.

Also preferably, the signal switching engine rotational speed isdisposed between a 0.5-order resonance region which is an enginerotational speed region where the resonance becomes a 0.5-orderresonance and a first-order resonance region which is an enginerotational speed region where the resonance becomes a first-orderresonance, and the frequency signal switching means outputs the secondand first frequency signals respectively in an engine rotational speedregion on the 0.5-order resonance region side of the signal switchingengine rotational speed and in an engine rotational speed region on thefirst-order resonance region side of the signal switching enginerotational speed.

Consequently, the fluctuation or resonance of the timer piston in thefirst-order and 0.5-order resonance regions can be eliminated.

Preferably, in this case, the signal switching engine rotational speedis set such that a rotational speed difference from a first-orderresonance engine rotational speed where the first-order resonance occurswith respect to the second frequency is greater than a rotational speeddifference from a 0.5-order resonance engine rotational speed where the0.5-order resonance occurs with respect to the first frequency.

Consequently, the fluctuation or resonance of the timer piston can beeliminated efficiently in the first-order resonance region where thedemand for suppressing the fluctuation or resonance is relatively high.

Also preferably, the signal switching engine rotational speed isdisposed between a first N-order resonance engine rotational speed wherean N-order resonance is generated with respect to the first frequencyand a second N-order resonance engine rotational speed where an N-orderresonance is generated with respect to the second frequency, and thefrequency signal switching means outputs the first and second frequencysignals respectively in an engine rotational speed region on the lowerrotational speed region side of the signal switching engine rotationalspeed and in an engine rotational speed region on the higher rotationalspeed region side of the signal switching engine rotational speed.

Consequently, the fluctuation or resonance of the timer piston in theN-order resonance regions can securely be eliminated.

Preferably, in this case, the signal switching rotational speed is setsuch that a rotational speed difference from the second N-orderresonance engine rotational speed is greater than a rotational speeddifference from the first N-order resonance engine rotational speed.

Consequently, in the case of the same-order resonance regions, thesecond frequency signal of a lower driving frequency attains a marginconcerning the engine rotational speed difference greater than that ofthe first frequency of a higher driving frequency, whereby thefluctuation or resonance can be eliminated efficiently in the case of alower frequency where it is likely to occur with a greater amplitude.

Preferably, the N is an integer or 0.5.

Also preferably, the signal switching engine rotational speed comprisesa first signal switching engine rotational speed disposed between afirst-order resonance region which is an engine rotational speed regionwhere the resonance becomes a first-order resonance and a second-orderresonance region which is an engine rotational speed region where theresonance becomes a second-order resonance, and a second signalswitching engine rotational speed disposed between a 0.5-order resonanceregion which is an engine rotational speed region where the resonancebecomes a 0.5-order resonance and a first-order resonance region whichis an engine rotational speed region where the resonance becomes afirst-order resonance; and the frequency signal switching means outputsthe second frequency signal in an engine rotational speed region on thefirst-order resonance region side of the first signal switching enginerotational speed and in an engine rotational speed region on the0.5-order resonance region side of the second signal switching enginerotational speed, and outputs the first frequency signal in an enginerotational speed region on the second-order resonance region side of thefirst signal switching engine rotational speed and in an engine speedregion on the first-order resonance region side of the second signalswitching engine rotational speed.

Consequently, the fluctuation or resonance of the timer piston in thefirst-order, 0.5-order, and second-order resonance regions can beeliminated.

Further preferably, in this case, the first signal switching enginerotational speed is set such that a rotational speed difference from afirst-order resonance engine rotational speed where the first-orderresonance occurs with respect to the first frequency is greater than arotational speed difference from a second-order resonance enginerotational speed where the second-order resonance occurs with respect tothe second frequency, and the second signal switching rotational speedis set such that a rotational speed difference from a first-orderresonance engine rotational speed where the first-order resonance occurswith respect to the second frequency is greater than a rotational speeddifference from a 0.5-order resonance engine rotational speed where the0.5-order resonance occurs with respect to the first frequency.

Consequently, while the fluctuation or resonance of the timer piston isefficiently eliminated in the first resonance region where the demandfor suppressing the fluctuation or resonance is relatively high, thefluctuation or resonance of the timer piston can be eliminated in the0.5-order and second-order resonance regions as well as in thefirst-order resonance region.

Also preferably, the signal switching engine rotational speed comprisesa first signal switching engine rotational speed disposed between afirst-order resonance region which is an engine rotational speed regionwhere the resonance becomes a first-order resonance and a second-orderresonance region which is an engine rotational speed region where theresonance becomes a second-order resonance, a second signal switchingengine rotational speed disposed between a 0.5-order resonance regionwhich is an engine rotational speed region where the resonance becomes a0.5-order resonance and a first-order resonance region which is anengine rotational speed region where the resonance becomes a first-orderresonance, a third signal switching engine rotational speed disposedbetween a first 0.5-order resonance engine rotational speed where a0.5-order resonance is generated with respect to the first frequency anda second 0.5-order resonance engine rotational speed where a 0.5-orderresonance is generated with respect to the second frequency, a fourthsignal switching engine rotational speed disposed between a firstfirst-order resonance engine rotational speed where a first-orderresonance is generated with respect to the first frequency and a secondfirst-order resonance engine rotational speed where a first-orderresonance is generated with respect to the second frequency, and a fifthsignal switching engine rotational speed disposed between a firstsecond-order resonance engine rotational speed where a second-orderresonance is generated with respect to the first frequency and a secondsecond-order resonance engine rotational speed where a second-orderresonance is generated with respect to the second frequency; and thefrequency signal switching means outputs the second frequency signal inan engine rotational speed region between the third and second signalswitching engine rotational speeds and in an engine rotational speedregion between the fourth and first signal switching engine rotationalspeeds, and outputs the first frequency signal in an engine rotationalspeed region between the second and fourth signal switching enginerotational speeds and an engine rotational speed region between thefirst and fifth signal switching engine rotational speeds.

Consequently, the fluctuation or resonance of the timer piston in thefirst-order, 0.5-order, and second-order resonance regions can securelybe eliminated.

Preferably, in this case, the first signal switching engine rotationalspeed is set such that a rotational speed difference from a first-orderresonance engine rotational speed where the first-order resonance occurswith respect to the first frequency is greater than a rotational speeddifference from a second-order resonance engine rotational speed wherethe second-order resonance occurs with respect to the second frequency,the second signal switching rotational speed is set such that arotational speed difference from a first-order resonance enginerotational speed where the first-order resonance occurs with respect tothe second frequency is greater than a rotational speed difference froma 0.5-order resonance engine rotational speed where the 0.5-orderresonance occurs with respect to the first frequency, the third signalswitching rotational speed is set such that a rotational speeddifference from the second 0.5-order resonance engine rotational speedis greater than a rotational speed difference from the first 0.5-orderresonance engine rotational speed, the fourth signal switchingrotational speed is set such that a rotational speed difference from thesecond first-order resonance engine rotational speed is greater than arotational speed difference from the first first-order resonance enginerotational speed, and the fifth signal switching rotational speed is setsuch that a rotational speed difference from the second second-orderresonance engine rotational speed is greater than a rotational speeddifference from the first second-order resonance engine rotationalspeed.

Consequently, while the fluctuation or resonance of the timer piston isefficiently eliminated in the first resonance region where the demandfor suppressing the fluctuation or resonance is relatively high, andwhile the second frequency signal of a lower driving frequency attains amargin concerning the engine rotational speed difference greater thanthat of the first frequency of a higher driving frequency, thusefficiently suppressing the fluctuation or resonance of the timer pistonin the case of a lower frequency where greater suppression is desired,the fluctuation or resonance of the timer piston in the 0.5-order andsecond-order resonance regions can be eliminated as well as in thefirst-order resonance region.

Further preferably, the frequency signal switching means outputs thefirst frequency signal in an engine rotational speed region on the lowerrotational speed side of the third signal switching engine rotationalspeed.

Consequently, the fluctuation or resonance of the timer piston in the0.5-order resonance can securely be eliminated in lower enginerotational speed regions.

Further preferably, the frequency signal switching means outputs thesecond frequency signal in an engine rotational speed region on thehigher rotational speed side of the fifth signal switching enginerotational speed.

Consequently, the fluctuation or resonance of the timer piston in thesecond-order resonance can securely be eliminated in higher enginerotational speed regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a control block diagram showing the configuration of mainparts of an engine fuel injection timing control apparatus in accordancewith an embodiment of the present invention;

FIG. 2 is a view showing a driving control model of a timer pistonconcerning the engine fuel injection timing control apparatus inaccordance with an embodiment of the present invention;

FIG. 3 is a view for explaining operations of the engine fuel injectiontiming control apparatus in accordance with an embodiment of the presentinvention;

FIG. 4 is a sectional view showing a fuel injection pump of a dieselengine;

FIG. 5(A) is a sectional view showing a timer of the fuel injection pumpof the diesel engine in a state before the fuel injection timing isadjusted to the advancing side;

FIG. 5(B) is a sectional view showing a timer of the fuel injection pumpof the diesel engine in a state after the fuel injection timing isadjusted to the advancing side;

FIG. 6 is a graph showing experimental data concerning a fluctuationphenomenon which is a problem to be overcome by the present invention;

FIG. 7 is a graph showing results of simulation concerning a fluctuationphenomenon which is a problem to be overcome by the present invention;

FIG. 8 is a view showing the prior art while illustrating a relationshipbetween the driving frequency of a timing control valve and the enginerotation; and

FIG. 9 is a view showing an amplitude characteristic of a timer pistonupon the fluctuation phenomenon with respect to the frequency differencebetween the driving frequency of the timing control valve and the enginerotation for each control frequency of the timing control valve.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to the drawings, embodiments of the present inventionwill be explained hereinafter.

FIGS. 1 to 3 show, in accordance with an embodiment of the presentinvention, an engine fuel injection timing control apparatus, which isapplicable to a distributor type fuel injection pump based on anelectronic control system such as that shown in FIGS. 4, 5(A), and 5(B),as explained above as the prior art. Accordingly, with reference toFIGS. 4, 5(A), and 5(B), this distributor type fuel injection pump willbe briefly explained at first.

As shown in FIG. 4, the fuel injection pump equipped with the enginefuel injection timing control apparatus comprises, within a pump mainbody 10, a vane type feed pump 11 which is rotated by an engine-drivendrive shaft 12. The feed pump 11 forcibly feeds fuel from a fuel tank toa pump chamber 13 within the pump main body 10, and further to a fuelforced feed plunger 15 through a passage 14. The passage 14 is providedwith a fuel cutting magnet valve 16.

The plunger 15 moves back and forth within a plunger chamber 17.According to the position of the plunger 15, the fuel on the passage 14side is taken into the plunger chamber 17 and is forcibly fed, by way ofa communicating hole 17A, through a passage 18 to a delivery valve 19.Here, each cylinder is provided with the passage 18 and the deliveryvalve 19. The plunger 15 is driven so as to move back and forth by a camdisc 20 attached to one end thereof.

Namely, the cam disc 20 is urged, by a spring 21 attached to the plunger15, against a roller 23 which is axially supported by a roller holder22. When the plunger 15 and the cam disc 20 are rotated by the driveshaft 12, the cam disc 20 moves in the axial direction while beingshoved by the roller 23 according to its cam profile, thereby moving theplunger 15 back and forth, thus supplying the fuel at a desired timing.

As shown in FIGS. 5(A) and 5(B), the roller holder 22 is provided with aplurality of rollers 23 (which are four here), and the cam disc 20 has acam profile corresponding thereto. Consequently, as the cam disc 20makes one revolution, the plunger 15 is driven four times, whereby, forexample, fuel is successively supplied to four cylinders respectively inresponse to these four driving operations of the plunger 15.

Also provided are not only a control sleeve 24 for fuel injection amountcontrol, and a governor (electric governor here) 25 for controlling thecontrol sleeve 24; but also a regulator valve 26, a sensing gear plate27 for detecting the rotational speed (number of revolution per unittime) of the drive shaft 12, a fuel temperature sensor 28, and anoverflow valve 29, provided with a check valve, for returning excessfuel within the pump chamber 13 to the fuel tank.

Further provided is a timer 30 equipped with a timer piston 31 forchanging the position of the roller 23 in its rotating direction. Asshown in FIGS. 4, 5(A), and 5(B), the timer piston 31 minutely rotatesthe roller holder 22 via a piston pin 33 while moving back and forthwithin a cylinder 32 formed in the pump main body 10.

The timer piston 31 has an intermediate portion to which the piston pin33 is connected, one end provided with a first pressure chamber 34 intowhich the fuel pressure within the pump chamber 13 is introduced, andthe other end provided with a second pressure chamber 35 into which theintake-side fuel pressure (fuel pressure upstream the feed pump 11) isintroduced. Consequently, for example, when the fuel pressure within thefirst pressure chamber 34 becomes higher than that in the state shown inFIG. 5(A), the timer piston 31 moves to the left in the drawing as shownin FIG. 5(B), whereby the fuel injection timing is adjusted to theadvancing side. When the fuel pressure within the first pressure chamber34 becomes low, by contrast, the timer piston 31 moves to the right inthe drawing, whereby the fuel injection timing is adjusted to theretarding side.

Also, the timer piston 31 is provided with a passage 36 through whichthe pump chamber 13 and the first pressure chamber 34 communicate witheach other, and the passage 36 is formed with an orifice 37. Further,disposed within the second pressure chamber 35 is a timer spring 38 forurging the timer piston 31 toward the one end (toward the first pressurechamber 34).

Hence, the position of the timer piston 31 is determined according tothe balance among the fuel pressure within the first pressure chamber34, the fuel pressure within the second pressure chamber 35, and theurging force of the timer spring 36. In the case of this pump, as shownin FIG. 4, there is provided a timing control valve (TCV) 39 which, as atimer controlling solenoid valve, can adjust the pressure balancebetween the first pressure chamber 34 side and the second pressurechamber 35 side, whereby the fuel injection timing can be adjusted onthe basis of various parameters.

The timing control valve 39 is a solenoid valve of electronic controltype, whose opening (valve opening time per unit time) is adjusted byduty control. Accordingly, as the timing control valve 39 isduty-controlled, the pressure difference between the pressure on thefirst pressure chamber 34 side and the pressure on the second pressurechamber 35 side is appropriately adjusted (to the reducing side here)according to the opening of the valve 39, thus regulating the positionof the timer piston 31, whereby the fuel injection timing is adjusted.

Such driving of the timing control valve 39 is effected by currentcontrol on a timing control valve solenoid (TCV solenoid) 40A such asthat shown in FIG. 1. This current control is regulated by an ECU(electronic control unit) 41, as control means, according to a targetfuel injection amount Q and an engine rotational speed (i.e., number ofengine revolution per unit time, which will be hereinafter referred toas engine speed) Ne. The present fuel injection timing control apparatusis characterized by such driving control of the timing control valve 39,which will be explained after the driving control of the timer piston 31effected through the ECU 41 is explained with reference to a drivingcontrol model of the timer piston 31 shown in FIG. 2.

The position of the timer piston 31 is set where the pressure applied tothe higher-pressure first pressure chamber 34 side (pressure as thedifference between the pressure within the higher-pressure firstpressure chamber 34 and that within the lower-pressure second pressurechamber 35) and the spring force of the timer spring 38 exerted from thelower-pressure second pressure chamber side are in balance with eachother. The driving control of the timer piston 31 is effected from sucha viewpoint.

Namely, as shown in FIG. 2, assuming that the direction of the pressureacting on the timer piston 31 from the higher-pressure first pressurechamber 34 is positive, pressure P1 within the higher-pressure firstpressure chamber 34 (see B1) and original pressure fluctuation (pressureinfluence of fluctuating feed pump discharge pressure) P3 acting on thefirst pressure chamber 34 (see B3) are applied thereto in the positivedirection, whereas pressure P2 within the lower-pressure second pressurechamber 35 (see B2) is applied thereto in the negative direction.

Also, pressure control amount Pc from the first pressure chamber 34 tothe second pressure chamber 35 caused by the timing control valve 39decreases a positive pressure (see a1) and increases a positive pressure(see a2).

The flow rate of fuel entering the first pressure chamber 34 is inproportion to the square root of the pressure difference between thepump chamber 13 side and the timer cylinder 32 side (first pressurechamber 34 side) (see B5), and is obtained when it is multiplied by theflow coefficient (orifice coefficient) of the orifice 37 (see B6).Similarly, the amount of the fuel flowing out of the timer cylinder 32side (first pressure chamber 34 side) is in proportion to the squareroot of the difference between the cylinder pressure and the lowerpressure (see B2), while its flow rate changes according to the on/offstate of the timing control valve 39 (see B7). The position of the timerpiston 31 is determined by these inflow and outflow fuel amounts withrespect to the timer cylinder 32.

Consequently, when the timing control valve 39 is controlled so as tochange the inflow and outflow fuel amounts with respect to the timercylinder 32, the piston position changes. Hence, when the on/off ratio(i.e., duty cycle) of the timing control valve 39 is set according tothe engine speed Ne and the injection amount Q, the fuel injectiontiming can be controlled, and the fuel injection timing can further beduty-controlled by detecting the actual fuel injection timing.

For example, further processing operations such as those shown in FIG. 2(B8 to B15, a3 to a5, d1, and d2) may control the timer piston.

The driving control system for the timing control valve 39 itself by theECU 41 is configured as shown in FIG. 1.

Namely, the ECU 41 comprises a first frequency signal generating means42, a second frequency signal generating means 43, a frequency signalswitching means 44, a duty cycle determining means 45, a timing controlvalve control means 46, and a driving circuit 47.

The first frequency signal generating means 42 generates a signal Wlhaving a first frequency f₁ (e.g., 80 Hz), whereas the second frequencysignal generating means 43 generates a signal having a second frequencyf₂ (e.g., 60 Hz) lower than the first frequency f₁.

According to the engine speed Ne, the frequency signal switching means44 selectively outputs the first frequency signal f₁ and the secondfrequency signal f₂, which is effected so as to avoid resonance regionsbetween the timing control valve 39 and the engine as shown in FIG. 3.The frequency signal switching means 44 can be constituted by aselecting frequency judging means 44A and a switch 44B which changesover in response to a selecting signal from the selecting frequencyjudging means 44A. This switching control of frequency signals will beexplained later in detail.

The duty cycle determining means 45 determines the duty cycle of thetiming control valve (solenoid valve) 39 according to the operationstate of the engine, namely, it determines the duty cycle in response toa target position of the timer piston 31 (target piston position) set bya target piston position setting means 48. Here, the target pistonposition setting means 48 sets the target piston position on the basisof the fuel injection amount (fuel injection time) Q and the enginespeed Ne.

In this embodiment, the duty cycle determining means 45 sets anexcitation time (on-control time) t1 of a coil 39A of the timing controlvalve 39 corresponding to the duty cycle, for example, on the basis of amap.

Namely, once a duty cycle is set, the excitation time t₁ can be computedas a control period multiplied by this duty cycle. Here, since a firstcontrol period corresponding to the first frequency f₁ and a secondcontrol period corresponding to the second frequency f₂ are provided, afirst frequency map A corresponding to the first frequency f₁ and asecond frequency map B corresponding to the second frequency f₂ areprepared and appropriately used, so as to set the excitation time t₁corresponding to the duty cycle.

The control means 46 controls the timing control valve 39 on the basisof an on/off signal which has not only the frequency f₁ or f₂ based onthe signal outputted through the frequency signal switching means 44 butalso the on/off ratio (i.e., duty cycle) determined by the duty cycledetermining means 45.

Accordingly, as shown in FIG. 1, the control means 46 comprises azero-crossing detector 46A, a triangular wave generator 46B, acomparator 46C, and an AND circuit 46D.

Among them, the zero-crossing detector 46A, which detects zero-crossingof the frequency signal W1, outputs an on signal to the triangular wavegenerator 46B and the AND circuit 46D when the frequency signal W1 isfed therein, and outputs a detection signal to the triangular wavegenerator 46B when zero-crossing is detected.

The triangular wave generator 46B generates and outputs a triangularwave signal in response to the on signal from the zero-crossing detector46A, and this triangular signal is reset by the zero-crossing detectionsignal.

The comparator 46C compares an output level of the triangular wavesignal from the triangular wave generator 46B with an output level ofthe excitation time signal of the timing control valve 39 determined bythe duty cycle determining means 43. It outputs an on signal (excitationsignal) when the output level of the triangular wave signal is lowerthan that of the excitation time signal, whereas it outputs an offsignal (excitation terminating signal) when the output level of thetriangular wave signal is at least as high as that of the excitationtime signal.

Further, the AND circuit 46D outputs an on signal (excitation signal) tothe driving circuit 47 when an on signal is outputted from thezero-crossing detector 46A while the comparator 46C outputs an onsignal.

The driving circuit 47 comprises a power supply 47A and a transistor47B. Upon receiving an on signal from the AND circuit 46, the transistor47B, which functions as a switching circuit, supplies an electric powerfrom the power supply 47A to the coil 39A of the timing control valve 39so as to excite the coil.

Here, the switching control of frequency signals by the frequency signalswitching means 44 will be explained. While the switching control offrequency signals in the frequency signal switching means 44 is effectedso as to avoid resonance regions between the timing control valve 39 andthe engine as mentioned above, the resonance regions will be explainedat first.

Namely, the resonance regions between the timing control valve 39 andthe engine exist in the vicinity of points where the driving frequencyof the timing control valve coincides with integral multiples of theengine speed Ne. When the driving frequency of the timing control valveis not less than several ten Hz, there are 0.5-order, first-order, andsecond-order resonance points in a normal engine rotation region (whoseupper limit is on the order of 5,000 to 6,000 rpm).

Namely, of the resonance between the timing control valve 39 and theengine, typical is a case where the frequency of pressure fluctuation ofthe timing control valve 39 applied to the timer piston 31 (i.e.,driving frequency) completely coincides with the operating frequency ofthe reaction force generated when the cam disc runs over. It is thefirst-order resonance. In the case of a four-cylinder engine, thefrequency of the reaction force at the time when the cam disc runs overis twice that of the engine speed Ne, whereby the first-order resonanceoccurs when the driving frequency of the timing control valve 39 istwice as high as the engine speed Ne.

In addition, the resonance between the timing control valve 39 and theengine also occurs when the pressure fluctuation frequency (drivingfrequency) of the timing control valve 39 coincides with integralmultiples of the run-over reaction force frequency. The second-orderresonance refers to the case where the driving frequency of the timingcontrol valve 39 is twice that of the run-over reaction force frequency.In the case of a four-cylinder engine, the second-order resonance occurswhen the driving frequency of the timing control valve 39 is four timesas high as the engine speed Ne.

Further, in addition, the resonance between the timing control valve 39and the engine occurs when the run-over reaction force frequency of thecam disc coincides with integral multiples of the driving frequency ofthe timing control valve 39. The 0.5-order resonance refers to the casewhere the run-over reaction force frequency is twice that of the drivingfrequency of the timing control valve 39 (in other words, where thedriving frequency of the timing control valve 39 is 0.5 times that ofthe run-over reaction force frequency). In the case of a four-cylinderengine, the 0.5-order resonance occurs when the driving frequency of thetiming control valve 39 coincides with the engine speed Ne.

The "fluctuation phenomenon" generated in the timer piston 31 becomesproblematic at these 0.5-order, first-order, and second-order resonancepoints. In particular, as already explained with reference to FIG. 9,the piston amplitude caused by the "fluctuation phenomenon" in thefirst-order resonance region is substantially twice as large as that ofthe 0.5-order resonance region, and substantially four times as large asthat of the second-order resonance region.

Therefore, in order to respond to such characteristics, the frequencysignal switching means 44 switches frequency signals such that the"fluctuation phenomenon" in the first-order resonance region iseliminated in preference to that in the 0.5-order and second-orderresonance regions.

Also, the lower the frequency is, the greater becomes the amplitude offluctuation of the timer piston in the resonance regions of thesame-order. Accordingly, the frequency signal switching means 44 avoidsthe resonance region in the case where the driving frequency is low(i.e., case of the second frequency) in preference to the case where thedriving frequency is high (i.e., case of the first frequency).

Specifically, as shown in FIG. 3, the frequency signal switching means44 switches frequency signals at signal switching engine speeds(hereinafter referred to as switching speeds) N₁, N₂, N₃, N₄, and N₅.Namely, when the engine speed Ne detected by the selecting frequencyjudging means 44A in response to the detection information from a speedsensor (engine rotational speed detecting means) 49 for detecting theengine speed coincides with any of the switching speeds N₁ to N₅, thefrequency signals are switched.

Of the switching speeds N₁ to N₅, the switching speed N₁ (thirdswitching engine rotational speed) is disposed in the 0.5-orderresonance region, the switching speed N₂ (second switching enginerotational speed) is disposed between the 0.5-order and first-orderresonance regions, the switching speed N₃ (fourth switching enginerotational speed) is disposed in the first-order resonance region, theswitching speed N₄ (first switching engine rotational speed) is disposedbetween the first-order and second-order resonance regions, and theswitching speed N₅ (fifth switching engine rotational speed) is disposedin the second-order resonance region.

Also, the frequency signals are switched such that the first frequencyf₁ is used when the engine speed Ne is less than N₁, the secondfrequency f₂ is used when the engine speed Ne is at least N₁ but lessthan N₂, the first frequency f₁ is used when the engine speed Ne is atleast N₂ but less than N₃, the second frequency f₂ is used when theengine speed Ne is at least N₃ but less than N₄, the first frequency f₁is used when the engine speed Ne is at least N₁ but less than N₅, andthe second frequency f₂ is used when the engine speed Ne is at least N₅.

In particular, the individual switching speeds N₁, N₂, N₃, N₄, and N₅are set as follows.

Namely, assuming that the engine speeds at the 0.5-order, first-order,and second-order resonance points in the first frequency f₁ arerespectively N₁₁, N₁₂, and N₁₃, and that the engine speeds at the0.5-order, first-order, and second-order resonance points in the secondfrequency f₂ are respectively N₂₁, N₂₂, and N₂₃ ; differences L₁, L₂,L₃, L₄, L₅, U₁, U₂, U₃, U₄, and U₅ are formed between the switchingspeeds N₁, N₂, N₃, N₄, and N₅ and their adjacent resonance engine speedsN₁₁, N₁₂, N₁₃, N₂₁, N₂₂, and N₂₃. Here, these differences L₁, L₂, L₃,L₄, L₅, U₁, U₂, U₃, U₄, and U₅ can be defined as represented by thefollowing expressions:

    L.sub.1 =N.sub.1 -N.sub.21

    L.sub.2 =N.sub.22 -N.sub.2

    L.sub.3 =N.sub.3 -N.sub.22

    L.sub.4 =N.sub.23 -N.sub.4

    L.sub.5 =N.sub.5 -N.sub.23

    U.sub.1 =N.sub.11 -N.sub.1

    U.sub.2 =N.sub.2 -N.sub.11

    U.sub.3 =N.sub.12 -N.sub.3

    U.sub.4 =N.sub.4 -N.sub.12

    U.sub.5 =N.sub.13 -N.sub.5

Also, the switching speeds N₁, N₂, N₃, N₄, and N₅ are set so that suchdifferences L₁, L₂, L₃, L₄, L₅, U₁, U₂, U₃, U₄, and U₅ satisfy thefollowing expressions:

    N.sub.1 :L.sub.1 >U.sub.1                                  (1)

    N.sub.2 :L.sub.2 >U.sub.2                                  (2)

    N.sub.3 :L.sub.3 >U.sub.3                                  (3)

    N.sub.4 :U.sub.4 >L.sub.4                                  (4)

    N.sub.5 :L.sub.5 >U.sub.5                                  (5)

Among them, condition (1) concerning the setting of the switching speedN₁, condition (3) concerning the setting of the switching speed N₃, andcondition (5) concerning the setting of the switching speed N₅ areprovided in order to attain a greater margin (speed difference, i.e.,rotational speed difference) in the second frequency f₂ of the lowerdriving frequency than in the first frequency f₁ of the higher drivingfrequency in the case of the same-order resonance regions, so as toeliminate the former frequency from the resonance region morepreferentially.

Also, condition (2) concerning the setting of the switching speed N₂ andcondition (4) concerning the setting of the switching speed N₄ areprovided in order to attain a greater margin (speed difference, i.e.,rotational speed difference) in the case of the first-order resonanceregion than in the 0.5-order and second-order resonance regions, so asto avoid the former resonance region more preferentially.

Of course, the switching speeds N₁, N₂, N₃, N₄, and N₅ cannot bedetermined by such conditions alone. In practice, based on theseconditions, each of the ratio of L₁ to U₁, ratio of L₂ to U₂, ratio ofL₃ to U₃, ratio of L₄ to U₄, and ratio of L₅ to U₅ is set so that themagnitude of amplitude of the timer piston 31 is substantially uniformlylowered by the "fluctuation phenomenon." Such setting can appropriatelybe effected on the basis of test data.

Since the fuel injection timing control apparatus in accordance with anembodiment of the present invention is configured as mentioned above,when injecting the fuel, while setting a fuel injection timing and afuel injection time (injection amount) by the ECU 41, it drives the fuelinjection valve according to thus set fuel injection timing and fuelinjection time.

Though the fuel injection timing is controlled by the positionaladjustment of the timer piston 31, such positional adjustment iseffected by adjusting the oil pressure (fuel pressure) applied to thetimer piston 31 while the timing control valve 39 is duty-controlled.

This control of the timing control valve 39 is effected through thetimer control valve control means 46 as follows.

Namely, at the time of this control, the signal (first frequency signal)W1 having the first frequency f₁ is emitted from the first frequencygenerating means 42, whereas the signal (second frequency signal) W2having the second frequency f₂ lower than the first frequency f₁ isemitted from the second frequency generating means 43. Then, thefrequency signal switching means 44 selectively outputs the firstfrequency signal W1 from the first frequency signal generating means 42and the second frequency signal W2 from the second frequency signalgenerating means 43 while switching between them according to such acharacteristic as that shown in FIG. 3 in response to the engine speedNe.

On the other hand, the duty cycle determining means 45 determines a dutycycle according to the target position of the timer piston 31 (targetpiston position) and further sets, on the basis of a map correspondingto the frequency selected by the frequency signal switching means 44,the excitation time t₁ of the timing control valve 39 with respect tothe duty cycle and the driving period.

Then, the control means 46 receives from the duty cycle determiningmeans 45 an excitation signal corresponding to the excitation time,thereby outputting an on signal for the duration of the excitation timet₁ in each excitation period, thereby exciting the coil 39A of thetiming control valve 39 through the driving circuit 47.

Consequently, the timing control valve 39 is regulated to a desiredopening (time-average opening) so that the position of the timer piston31 is appropriately adjusted, whereby a desired fuel injection timing isattained.

A kind of beat phenomenon known as the "fluctuation" of the timer piston31 is generated when the driving frequency of the timing control valve39 approaches a resonance region with respect to the engine speed asmentioned above. In the present apparatus, as shown in FIG. 3, when thefrequency signal W1 approaches its resonance region, the frequencysignal is switched to the second frequency signal W2 that is relativelyseparated from this resonance region; and when the frequency signal W2approaches its resonance region, on the other hand, the frequency signalis switched to the first frequency signal W1 that is relativelyseparated from this resonance region. Consequently, the drivingfrequency of the timing control valve 39 does not approach the resonanceregion with respect to the engine speed, whereby the "fluctuation" ofthe timer piston 31 is eliminated or, if any, is suppressed to a smallamplitude. Of course, the resonance itself is eliminated.

In particular, though the "fluctuation" in the first-order resonanceregion is generated with an amplitude greater than that in the 0.5-orderor second-order resonance region; since the elimination of thefirst-order resonance region is effected in preference to that of the0.5-order and second-order resonance regions according to condition (2)concerning the setting of the switching speed N₂ and condition (4)concerning the setting of the switching speed N₄, the "fluctuation" inthe first-order resonance region is securely suppressed in response tothe highest demand existing there.

Further, though the "fluctuation" in the second frequency f₂ of a lowerdriving frequency is likely to occur with an amplitude greater than thatin the "fluctuation" in the first frequency f₁ of a higher drivingfrequency in the case of the same-order resonance regions; since theelimination of the second frequency f₂ of the lower driving frequencyfrom the resonance regions is effected in preference to that of thefirst frequency f₁ of the higher driving frequency in the case of thesame-order resonance regions according to condition (1) concerning thesetting of the switching speed N₁, condition (3) concerning the settingof the switching speed N₃, and condition (5) concerning the setting ofthe switching speed N₅, the "fluctuation" in the case of a lower drivingfrequency can securely be suppressed in response to a higher demandexisting there.

When the "fluctuation" is thus suppressed, the amplitude of vibration ofthe timer piston 31 caused by the "fluctuation" decreases, therebyallowing a sufficient accuracy in control of the fuel injection timingto be secured, thus advantageously being capable of contributing toimproving engine performances.

Also, the "fluctuation" can securely be suppressed by the switchingcontrol of only two kinds of driving frequencies, whereby theconfiguration of the control system can be simplified in terms of eitherhardware or software.

Further, the above-mentioned frequency switching speeds N₁ to N₅ cansecurely be set when "fluctuation" generating characteristics aredetected by a test and the like.

Capability of Exploitation in Industry

When the present invention is used for controlling an engine fuelinjection pump, such as a diesel-engine fuel injection pump, which cancontrol a fuel injection timing by adjusting the position of a timerpiston via a solenoid valve, the fluctuation phenomenon of the timerpiston occurring due to a relationship between the driving frequency ofthe timer controlling solenoid valve and the engine speed can besuppressed by simple control. Consequently, changes in the fuelinjection timing caused by the fluctuation in the timer piston can besuppressed easily, whereby the fuel injection timing can be controlledaccurately. Accordingly, it can contribute to improving engineperformances. Its utility is therefore considered to be extremely high.

I claim:
 1. In an engine fuel injection control apparatus comprising:atimer (30) for changing a fuel injection timing of an engine injectingfuel from a fuel injection valve by moving a timer piston (31) inresponse to an oil pressure supplied thereto and a timer controllingsolenoid valve (39) for adjusting the oil pressure supplied to saidtimer (30) as being opened and closed by a driving signal having a dutycycle which is set according to an operation state of said engine, inwhich a resonance occurring in said timer piston (31) between driving bysaid timer controlling solenoid valve (39) and a fluctuationaccompanying a rotation of said engine is eliminated by a change infrequency of the driving signal of said the timer controlling solenoidvalve (39); an engine fuel injection timing control apparatuscomprising:first frequency signal generating means (42) for generatingand emitting a signal (W1) having a first frequency (f₁), secondfrequency signal generating means (43) for generating and emitting asignal (W2) having a second frequency (f₂) which is lower than saidfirst frequency (f₁), engine rotational speed detecting means (49) fordetecting a rotational speed (Ne) of said engine, frequency signalswitching means (44) for selectively outputting said first frequencysignal (W1) emitted from said first signal generating means (42) andsaid second frequency signal (W2) emitted from said second signalgenerating means (43) according to the engine rotational speed (Ne)detected by said engine rotational speed detecting means (49), andcontrol means (46), having a driving frequency based on the frequencysignal outputted from said frequency signal switching means (44), forcontrolling said timer controlling solenoid valve (39) by using thedriving signal having the duty cycle that is set according to theoperation state of said engine, wherein said frequency signal switchingmeans (44) is configured so as to change over between said firstfrequency signal (W1) and said second frequency signal (W2) according toa preset signal switching engine rotational speed (N₁, N₂, N₃, N₄, N₅),and wherein said signal switching engine rotational speed (N₁, N₂, N₃,N₄, N₅) is set to a level which yields a first predetermined rotationalspeed difference (U₁, U₂, U₃, U₄, U₅) from an engine rotational speed(N₁₁, N₁₂, N₁₃) where said resonance is generated with respect to saidfirst frequency (f₁) and a second predetermined rotational speeddifference (L₁, L₂, L₃, L₄, L₅) from an engine rotational speed (N₂₁,N₂₂, N₂₃) where said resonance is generated with respect to said secondfrequency (f₂).
 2. The engine fuel injection timing control apparatus ofclaim 1,wherein said signal switching engine rotational speed (N₄) isdisposed between a first-order resonance region which is an enginerotational speed region where said resonance becomes a first-orderresonance and a second-order resonance region which is an enginerotational speed region where said resonance becomes a second-orderresonance, and wherein said frequency signal switching means (44)outputs said second frequency signal (W2) and said first frequencysignal (W1) respectively in an engine rotational speed region on saidfirst-order resonance region side of said signal switching enginerotational speed (N₄) and in an engine rotational speed region on saidsecond-order resonance region side of said signal switching enginerotational speed (N₄).
 3. The engine fuel injection timing controlapparatus of claim 2,wherein said signal switching rotational speed (N₄)is set such that a rotational speed difference (U₄) from a first-orderresonance engine rotational speed (Nl₁₂) where said first-orderresonance occurs with respect to said first frequency (f₁) is greaterthan a rotational speed difference (L₄) from a second-order resonanceengine rotational speed (N₂₃) where said second-order resonance occurswith respect to said second frequency (f₂).
 4. The engine fuel injectiontiming control apparatus of claim 1,wherein said signal switching enginerotational speed (N₂) is disposed between a 0.5-order resonance regionwhich is an engine rotational speed region where said resonance becomesa 0.5-order resonance and a first-order resonance region which is anengine rotational speed region where said resonance becomes afirst-order resonance, and wherein said frequency signal switching means(44) outputs said second frequency signal (W2) and said first frequencysignal (W1) respectively in an engine rotational speed region on said0.5-order resonance region side of said signal switching enginerotational speed (N₂) and in an engine rotational speed region on saidfirst-order resonance region side of said signal switching enginerotational speed (N₂).
 5. The engine fuel injection timing controlapparatus of claim 4,wherein said signal switching rotational speed (N₂)is set such that a rotational speed difference (L₂) from a first-orderresonance engine rotational speed (N₂₂) where said first-order resonanceoccurs with respect to said second frequency (f₂) is greater than arotational speed difference (U₂) from a 0.5-order resonance enginerotational speed (N₁₁) where said 0.5-order resonance occurs withrespect to said first frequency (f₁).
 6. The engine fuel injectiontiming control apparatus of claim 1,wherein said signal switching enginerotational speed (N₁, N₃, N₅) is disposed between a first N-orderresonance engine rotational speed (N₁₁, N₁₂, N₁₃) where an N-orderresonance is generated with respect to said first frequency (f₁) and asecond N-order resonance engine rotational speed (N₂₁, N₂₂, N₂₃) wherean N-order resonance is generated with respect to said second frequency(f₂), and wherein said frequency signal switching means (44) outputssaid first frequency signal (W1) and said second frequency signal (W2)respectively in an engine rotational speed region on the lowerrotational speed region side of said signal switching engine rotationalspeed (N₁, N₃, N₅) and in an engine rotational speed region on thehigher rotational speed region side of said signal switching enginerotational speed (N₁, N₃, N₅).
 7. The engine fuel injection timingcontrol apparatus of claim 6,wherein said signal switching rotationalspeed (N₁, N₃, N₅) is set such that a rotational speed difference (L₁,L₃, L₅) from said second N-order resonance engine rotational speed (N₂₁,N₂₂, N₂₃) is greater than a rotational speed difference (U₁, U₃, U₅)from said first N-order resonance engine rotational speed (N₁₁, N₁₂,N₁₃).
 8. The engine fuel injection timing control apparatus of claim 6,wherein said N is an integer.
 9. The engine fuel injection timingcontrol apparatus of claim 7, wherein said N is an integer.
 10. Theengine fuel injection timing control apparatus of claim 6, wherein saidN is 0.5.
 11. The engine fuel injection timing control apparatus ofclaim 7, wherein said N is 0.5.
 12. The engine fuel injection timingcontrol apparatus of claim 6, wherein said N is any of 0.5 and integers.13. The engine fuel injection timing control apparatus of claim 7,wherein said N is any of 0.5 and integers.
 14. The engine fuel injectiontiming control apparatus of claim 1,wherein said signal switching enginerotational speed comprises:a first signal switching engine rotationalspeed (N₄) disposed between a first-order resonance region which is anengine rotational speed region where said resonance becomes afirst-order resonance and a second-order resonance region which is anengine rotational speed region where said resonance becomes asecond-order resonance, and a second signal switching engine rotationalspeed (N₂) disposed between a 0.5-order resonance region which is anengine rotational speed region where said resonance becomes a 0.5-orderresonance and a first-order resonance region which is an enginerotational speed region where said resonance becomes a first-orderresonance; and wherein said frequency signal switching means (44)outputs said second frequency signal (W2) in an engine rotational speedregion on said first-order resonance region side of said first signalswitching engine rotational speed (N₄) and in an engine rotational speedregion on said 0.5-order resonance region side of said second signalswitching engine rotational speed (N₂), and outputs said first frequencysignal (W1) in an engine rotational speed region on said second-orderresonance region side of said first signal switching engine rotationalspeed (N₄) and in an engine rotational speed region on said first-orderresonance region side of said second signal switching engine rotationalspeed (N₂).
 15. The engine fuel injection timing control apparatus ofclaim 14,wherein said first signal switching engine rotational speed(N₄) is set such that a rotational speed difference (U₄) from afirst-order resonance engine rotational speed (N₁₂) where saidfirst-order resonance occurs with respect to said first frequency (f₁)is greater than a rotational speed difference (L₄) from a second-orderresonance engine rotational speed (N₂₃) where said second-orderresonance occurs with respect to said second frequency (f₂), and whereinsaid second signal switching rotational speed (N₂) is set such that arotational speed difference (L₂) from a first-order resonance enginerotational speed (N₂₂) where said first-order resonance occurs withrespect to said second frequency (f₂) is greater than a rotational speeddifference (U₂) from a 0.5-order resonance engine rotational speed (N₁₁)where said 0.5-order resonance occurs with respect to said firstfrequency (f₁).
 16. The engine fuel injection timing control apparatusof claim 1,wherein said signal switching engine rotational speed (N₁,N₂, N₃, N₄, N₅) comprises:a first signal switching engine rotationalspeed (N₄) disposed between a first-order resonance region which is anengine rotational speed region where said resonance becomes afirst-order resonance and a second-order resonance region which is anengine rotational speed region where said resonance becomes asecond-order resonance, a second signal switching engine rotationalspeed (N₂) disposed between a 0.5-order resonance region which is anengine rotational speed region where said resonance becomes a 0.5-orderresonance and a first-order resonance region which is an enginerotational speed region where said resonance becomes a first-orderresonance, a third signal switching engine rotational speed (N₁)disposed between a first 0.5-order resonance engine rotational speed(N₁₁) where a 0.5-order resonance is generated with respect to saidfirst frequency (f₁) and a second 0.5-order resonance engine rotationalspeed (N₂₁) where a 0.5-order resonance is generated with respect tosaid second frequency (f₂), a fourth signal switching engine rotationalspeed (N₃) disposed between a first first-order resonance enginerotational speed (N₁₂) where a first-order resonance is generated withrespect to said first frequency (f₁) and a second first-order resonanceengine rotational speed (N₂₂) where a first-order resonance is generatedwith respect to said second frequency (f₂), and a fifth signal switchingengine rotational speed (N₅) disposed between a first second-orderresonance engine rotational speed (N₁₃) where a second-order resonanceis generated with respect to said first frequency (f₁) and a secondsecond-order resonance engine rotational speed (N₂₃) where asecond-order resonance is generated with respect to said secondfrequency (f₂); and wherein said frequency signal switching means (44)outputs said second frequency signal (W2) in an engine rotational speedregion between said third signal switching engine rotational speed (N₁)and said second signal switching engine rotational speed (N₂) and in anengine rotational speed region between said fourth signal switchingengine rotational speed (N₃) and said first signal switching enginerotational speed (N₄), and outputs said first frequency signal (W1) inan engine rotational speed region between said second signal switchingengine rotational speed (N₂) and said fourth signal switching enginerotational speed (N₃) and an engine rotational speed region between saidfirst signal switching engine rotational speed (N₄) and said fifthsignal switching engine rotational speed (N₅).
 17. The engine fuelinjection timing control apparatus of claim 16,wherein said first signalswitching engine rotational speed (N₄) is set such that a rotationalspeed difference (U₄) from the first-order resonance engine rotationalspeed (N₁₂) where said first-order resonance occurs with respect to saidfirst frequency (f₁) is greater than a rotational speed difference (L₄)from the second-order resonance engine rotational speed (N₂₃) where saidsecond-order resonance occurs with respect to said second frequency(f₂), wherein said second signal switching rotational speed (N₂) is setsuch that a rotational speed difference (L₂) from the first-orderresonance engine rotational speed (N₂₂) where said first-order resonanceoccurs with respect to said second frequency (f₂) is greater than arotational speed difference (U₂) from the 0.5-order resonance enginerotational speed (N₁₁) where said 0.5-order resonance occurs withrespect to said first frequency (f₁), wherein said third signalswitching rotational speed (N₁) is set such that a rotational speeddifference (L₁) from said second 0.5-order resonance engine rotationalspeed (N₂₁) is greater than a rotational speed difference (U₁) from saidfirst 0.5-order resonance engine rotational speed (N₁₁), wherein saidfourth signal switching rotational speed (N₃) is set such that arotational speed difference (L₃) from said second first-order resonanceengine rotational speed (N₂₂) is greater than a rotational speeddifference (U₃) from said first first-order resonance engine rotationalspeed (N₁₂), and wherein said fifth signal switching rotational speed(N₅) is set such that a rotational speed difference (L₅) from saidsecond second-order resonance engine rotational speed (N₂₃) is greaterthan a rotational speed difference (U₅) from said first second-orderresonance engine rotational speed (N₁₃).
 18. The engine fuel injectiontiming control apparatus of claim 16,wherein said frequency signalswitching means (44) outputs said first frequency signal (W1) in anengine rotational speed region on the lower rotational speed side ofsaid third signal switching engine rotational speed (N₁).
 19. The enginefuel injection timing control apparatus of claim 16,wherein saidfrequency signal switching means (44) outputs said second frequencysignal (W2) in an engine rotational speed region on the higherrotational speed side of said fifth signal switching engine rotationalspeed (N₅).